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The bar joint mandibular denture
THE
BAR
JOINT
MANDIBULAR
DENTURE
EUGEN J. DOLDER, DR. MED. BENT.”
University
of
Zurich, Dental Institute, Zurich, Switzerland
OF STABILITY AND RETENTION of mandibular complete dentures a solution that is universally satisfactory, especially for patients with extensive alveolar bone resorption. The smaller the number of mandibular teeth that remain, the more thoughtfully these teeth should be treated. When only two natural teeth remain, a method of preserving them is imperative. This situation occurs most frequently in three arrangements (Fig. 1) : (1) two spaced teeth in the anterior region, such as the two cuspids, (2) two adjacent teeth in the anterior segment, such as one cuspid and the adjoining lateral incisor, and (3) two spaced teeth in one posterior segment of the dental arch, such as a second molar and a premolar. The bar joint denture preserves a small number of residual teeth as long as possible. The bar splints the shortened and crowned abutment teeth, retains and partially supports the complete denture, and, together with the sleeve contained in the denture base, acts as a joint.
T is far from
HE PROBLEM
PRINCIPALOFSHORTENINGTEETH
A statically unfavorable ratio exists between the length of the crown and the length of the root in most older patients. The supported root is relatively too short (Fig. 2). Often, in addition the long isolated crown is not stabilized by adjacent teeth. Therefore, residual teeth often respond to masticatory stresses with increased mobility. However, in many instances, teeth with decayed crowns, even with the loss of vital pulp tissue, and mobile teeth can be used as abutments if the coronal parts are reduced and the roots are protected with Richmond copings (Fig. 3). Radical shortening of such teeth results in a statically more favorable ratio of the length of the crown to the length of the root and avoids further breakdown of the periodontal structures. Endodontic treatment is performed at the same time if the remaining teeth are vital. In this stage, a pulpless tooth with a well-functioning periodontium is much more important than a loose tooth with a vital pulp. PRINCIPLEOFSPLINTING
Two teeth standing separately, such as the two lower cuspids, are splinted with a straight bar attached to the two Richmond copings. The bar is positioned as close to the residual alveolar ridge as possible. Both teeth become more firm and are safer abutments periodontally than if left standing alone (Fig. 4). *Professor
of Prosthetics; Head of the Department of Fixed Partial Dentures. 689
J. Pras. Den. July-August. 1961
DOLDER
c.
R
A.
Fig. l.-Different groups of remaining teeth permit the construction of the bar joint denture. A, Two spaced anterior teeth. B, Two adjacent anterior teeth. C, Two spaced posterior teeth.
Adjacent teeth are splinted by soldering mounted on top of the copings (Fig. 5). ELEMENTS
the copings together;
the bar is
Of THE RAR JOINT
The composite bar joint is made up of the bar and the sleeve (Fig. 6). The bar consists of a straight urought wire that is egg shaped in cross section. The bar connects and splints the abutment teeth by attachment to the copings and, at the same time, functions as the shaft part of a hinge joint. The bar is always oriented with its tapered edge adjacent to the residual alveolar ridge. The bar measures 3 mm. on its major and 2.2 mm. on its minor diameter; the “microbar” measures 2.3 mm. and 1.6 mm., respectively (Fig. 6 ) _ The open-sided sleeve, which is contained invisibly in the denture base, snaps over the bar when the denture is inserted. The sleeve is a 0.2 mm. thick gold alloy
n k’@. Z--.1,
c.
The two remaining cuspids exhibit extensively decayed crowns. B and C, Roentgenograms reveal supporting bone only along a small part of the roots.
BAR JOINT
Fig.
3 .-The
remaining
teeth
are
MANDIBULAR
radically shortened, Richmond copings.
DENTURE
and
the
691
roots
are
protected
with
Fig. 4.-The two Richmond copings with parallel pins are splinted solidly by the bar. The bar is notched somewhat mesially to the copings to free the gingival crest. The open-sided sleeve, cut obliquely at the ends for the same reason, is fitted tightly between the two copings.
sheet. The sleeve fits the broad top of the bar exactly but does not quite touch the tapering sides of the bar with its elastic flanges. FUNCTIONS
OF THE BAR JOINT
The bar and sleeve joint gives retention and guides the movements of the denture relative to the abutment teeth. The sleeve supplies functionally adequate retention, and when the teeth are out of contact, there is a vertical gap of about 1 mm. between the roof of the sleeve and the top of the bar (Fig. 6). From this initial (resting) position, the bar and sleeve joint permits three possible movements of the denture : (1) during vertical depression of the denture, the entire sleeve is translated toward or upon the bar, (2) during unilateral depression of the denture, only the more depressed end of the sleeve touches the bar, and (3) rotation about the bar as an axis is possible for approximately 10 degrees in either direction from the resting position. Rotation is limited only gradually by the elastic flanges of the sleeves (Fig. 6). MATERIAL
The alloys for all components of the bar joint should provide the requisite mechanical characteristics, including permanent elasticity of the sleeve. I use a high quality, platinum-containing alloy of gold.* *The Scientific
Dental Co., Ltd., Los Angeles, Calif.
J. Pros. Den. July-August, 1961
DOLDER
69 :!
Fig. B.-The
bar is mounted on top of two adjacent abutment
roots
Fig. G.---The bar joint in schematic cross section shows, from left to right: the parts disnssembled, insertion of the denture, the position of rest, perpendicular depression of the whole denture. and rotation about the bar as an axis.
4.
B.
F’ia. i.--&4. Low Richmond copings with long pins are used on long roots. copings on short roots require, in addition to short pins, a central inlay preparation lir~v!ration of the root for adequate retention.
B, Richmond and a higher
Construction tarp’a har joint denture when only the lower cuspids remain ilin-:trates the procedures. i~Ind,doutic treatment is iollowrtl 1)~ shortening and preparation of the abutIIIC’III>, iitting of pins ( which must be parallels, making of individual copper hand impressions with pills. and temporary sealing of the roots. Copings are waxed 1111 ~qqw-plated dies, invested, and cast around the pins, which are then soldered :ogerl~r. ShJrt roots with consequentlv short pins should be prepared somewhat Iiig-!wr am1 possibly with an interior re&orcing inlay preparation to achieve good rtwniion of the copings (Fig. 7 1,
BAR ,JOINT
Fig. K-The
MANDIBULAR
copings are positioned
DENTURE
in the individual
693
plaster impression.
An individual acrylic resin impression tray is prepared on a preliminary lower cast. Sufficient space is provided for the Richmond copings. The tray is fitted in the mouth, and the borders are developed in the same manner as for complete dentures. The Richmond copings are placed on the abutment teeth, and a plaster impression is made. The copings are positioned in the impression (Fig. 8) I An impression of the upper jaw is made if a maxillary complete denture is to be constructed at the same time. After the casts are poured, occlusion rims are constructed. The jaw relation records are made, and the teeth are selected.
Fig. 9.-A,
The labial
plaster
key contains
the anterior the cast.
teeth.
B,
The key
is positioned
on
The teeth are positioned in the occlusion rims. Acrylic resin teeth are used in the lower anterior segment so they can be arranged directly above the residual alveolar ridge. The try-in is completed. The position of the lower anterior teeth is recorded with a labial plaster core, and the anterior segment of the wax pattern is removed. The teeth are left fixed in the plaster key (Fig. 9). The bar is fitted between the two abutment copings on the cast and positioned horizontally with the tapered edge toward and close to the alveolar ridge, at right angles to the line bisecting the angle formed by the posterior alveolar ridges (Fig. 10). An oblique position of the bar impairs correct function
J. Pros. Den. July-August, 1961
1mL,Ixm
Fig.
IO.-The
Fig. 11 .-The
l;ig
1?,-.4
bar is positioned
horizontal
positioning
perpendicularly posterior
to a line ridges.
bisecting
of the bar and sleeve is important. R, The correct position.
the
angle
between
.4, The incorrect
schematic cross section of the anterior part of the cast illustrates the position bar and sleeve relative to the alveolar ridge and the artificial teeth.
Fig. 1X-The
soldered bar-copings
framework
is reseated onto the cast.
the
position.
of the
BAR JOINT
Fig. 14.-Three
dovetailed
MANDIBULAR
DENTURE
flaps are cut into the open-sided sleeve and bent up to supply tion in the acrylic resin denture base.
695
reten-
Fig. 15.
Fig. 16. Fig. 15.-The sleeve is fixed temporarily on the bar in the resting position by an intermediary wire. Fig. 16.-The copings are covered with a 1 mm. layer of plaster prior to curing the denture. Unimpaired functioning of the bar joint is not possible when the denture base flts the copings closely.
Fig 17.-An enlarged schematic cross section of the bar joint shows, from top to bottom: retentive Raps of the sleeve, the intermediary wire, the bar, the sleeve, and the plaster which assures the correct position of the sleeve during curing of the denture and creates space that is needed for proper functioning of the bar joint.
DOLDER
J. Pros. Den. July-August, 1961
of the joint (Fig. 11). The microbar is used only where there is insufficient interocclusal clearance for the regular size bar. The bar is temporarily attached to the cast with sticky wax or self-curing resin, and the plaster key containing the anterior teeth is carefully repositioned. The position of teeth determines whether or not the bar must be repositioned further lingually (Fig. 12). The final position of the bar and the copings is determined on the cast and secured with plaster. The bar and copings are solidly soldered and replaced on the cast, and the clearance between the bar and the mesial gingival papilla is determined (Fig. 13). An appropriate length of the metal sleeve is cut, and dovetailed flaps are bent up for retention in the denture base. No soldering is required, and thus the elasticity of the sleeve is fttlly maintained (Fig. 34). An auxiliary wire is placed between the top of the bar and the sleeve to maintain their position during the curing of the denture ( Fig. 15 I
pig.
‘ig.
‘ig.
Fig. IX.-The anterior teeth are delinitely wpositioned with the plaster key. Fig. 19.-A small lingual bar is adapted to reinforce the denture base. Fig. 2K-The functioning and the retention of the bar joint are tested outside
the mouth.
Volume I1 Number 4
BAR JOINT
Fig. Zl.-The
denture
Fig. 22.-The
Fig. 23.-The
MANDIBULAR
DENTURE
base above the abutment copings must be sufficiently free movement of the bar joint.
cemented copings with the connecting
697
excavated
to allow
bar are placed in the mouth.
elastic flanges of the egg-shaped sleeve may be tightened with instrument for better retention of the finished denture.
a suitable
pointed
The Richmond copings are covered with a 1 mm. layer of plaster (Fig. 16), and the space between the alveolar ridge and the flanges of the sleeve is also filled with plaster to maintain space in the denture base (Fig. 17). The anterior teeth are repositioned on the cast using the plaster key (Fig. 18), and the wax pattern of the denture is completed with a reinforcing lingual bar (Fig. 19). The flasking is completed in the usual manner. After processing, the denture is carefully deflasked; especially the bar must be cautiously removed from the sleeve.
598
J. Pros. Den. July-August, 1961
DOLDER
The anterior lingual part of the denture is made as thin as possible. Free functioning of the joint is tested outside the mouth with the bar-copings framework inserted into place in the denture base (Fig. 20). The denture base may need additional relief above the Richmond copings (Fig. 21) . The bar-copings framework is trial fitted in the mouth; slight grinding of the pins may be necessary to ensure correct, parallel seating (Fig. 22). Roentgenographic examination of the abutments and temporarily seated copings is required to establish the proper fit. The free flanges of the sleeve are tightened if the finished denture lacks adequate retention (Fig. 23). The occlusion is carefully balanced. Adjustment appointments are given the patient for 1 and 4 weeks after insertion. At the same time, the instructions to the patient regarding cleansing are repeated. IrYKhMICS
OF THE
BAR
JOINT
DENTURE
The mandibular bar joint denture is a complete denture on a fixed partial denture (microbridge) supported by terminal abutments. The bar and the sleeve
Fig. 2~1. Fig. 24.-A schematic cross section resting go&ion. Note the vertical gap bar. Fig. 25.-A schematic cross section vertically depressed position. Note that
Fig. 25.
shows the anterior part of the completed denture in its of about 1 mm. between the roof of the sleeve and the shows the anterior part of the completed denture in a the “roof” of the sleeve touches the top of the bar.
Fig. Z&---In a recently inserted bar joint denture, there is a vertical gap of about. 1 mm. between the bar and the roof of the embracing sleeve. Unilateral depression of the denture results in hinge movement about the axis (R) somewhere in the ridge of the undepressed side. Only the more depressed end of the sleeve touches the bar, while the opposite end remains near its resting position. The rotating system may be called a one-sided lever system.
Volume 11 Number 4
BAR JOINT
MANDIBULAR
DENTURE
699
serve as the connecting elements of the two dentures. The fixed partial denture consists essentially of the bar that is attached to the abutment copings. This constitutes the male part of the complete restoration. The female part, the sleeve, is contained in the base of the removable complete denture. The insertion and removal of the denture are accomplished easily by the patient. The elastic flanges of the sleeve readily snap over the egg-shaped bar and give the denture adequate retention. Position of Rest.-The inserted denture rests on the alveolar ridges and is entirely tissue borne. In this rest position, the roof of the sleeve is about 1 mm. above the top of the bar (Fig. 24). Vertical Translation.-When the denture is depressed vertically, it presses upon the resilient mucosa of the posterior ridges. The entire length of the sleeve approaches and then is depressed onto the bar transmitting part of the masticatory load onto the abutment teeth (Fig. 25). Th us, in the final phase of vertical depression, the denture is supported partly by the abutments and partly by the soft tissue. A well-retained and well-guided denture that transmits part of the masticatory load to anterior abutment teeth is appreciated by the patient, particularly during use of the anterior teeth.
Fig. 27.-A long bar ensures better guidance and retention of the denture than a short bar. Note the favorable lever diagram of the more nearly parallel posterior ridges (A) as compared to the diverging posterior ridges [B).
Fig. 28.-After the process of adaptation, the denture has embedded itself into the tissue approximately 1 mm., and the sleeve rests on the bar in its entire length in the resting position at this time. The hinge axis of a unilateral depression of the denture is now the coping of the depressed side, while the opposite side of the denture is slightly lifted from the mucosa. The rotating system may now be called a two-sided lever system.
J. Pros. Den. July-hugust, 1961
Fig. PR.-The
posteriorly
depressed denture rotates about the bar as its axis.
I!nilateral L)epressiolj.--The bar and sleeve permit the unilateral depression of the denture when it occurs during unilateral mastication. The denture rotates about the undepressed ridge as an axis, and the corresponding end of the sleeve remains near its rest position. Only the loaded end of the sleeve is depressed toward the bar (Fig. 26j. The longer the bar and the sleeve can he made, the better are the retention and the guidance of a denture subjectecl to such rotation (Fig. 27). In the course of 6 to 12 months, the denture embeds itself approximately 1 mm. into the mucosa, allowing the sleeve to rest directly upon the bar. The axis of rotation in unilateral depression of the clcnture is then transferred to the loaded el~d of the sleeve, and unilateral depression results in a slight lifting of the denture from the mucosa of the opposite side (Fig. 28 ) .
Fig. XJ.--The undesirable movements 01’ the denture are impeded by the bar joint: (‘a) lateral Imnslation; (RJ sagittal translation: (~1 horizontal rotation about a rertic*al axis in the anterior rvni9!i.
i’os~c~~io~I,c,fi~c,ssiolr.--Cl~e~~ing on the posterior part of the denture results in rot:ltion about the bar, its axis. This rotation is possible about any axis throughout tl~ continuum of axes within the perpendicular translation (Fig. 29). .I11 of these motions of the denture occur normally during mastication. The eggshaped structure of the bar joint permits these three movements and guides the rlc:lturt> effectivell,. However. the construction of the bar joint eliminates undexir:Ale movernent~ of the denture which are ultimately destructive (Fig. 30). I,atrral translatory movements hasten alveolar atrophy of the posterior ridges. The flatter the ridges are initially, the more care should be taken to impede lateral
Volume 11
BAR JOINT
Number 4
MANDIBULAR
DENTURE
701
translatory movements. A correctly fitted sleeve that touches both copings makes lateral displacement of the denture impossible. Forward and backward translations are withstood by the snugly fitting sleeve. Such movements can also be minimized by extending the denture base distally onto the retromolar pads. Rotation about a vertical axis in the anterior region is primarily destructive to the posterior ridges and impairs masticatory efficiency because the denture escapes the chewing force. Efficiency of chewing and stability of the denture are again to some degree dependent on the length of the bar and sleeve (Fig. 31). Extending the denture base into the mylohyoid region decreases the tendency of the denture to make such rotations.
Fig. 31.-A
long sleeve (A) hinders
ARRANGEMENT
rotation about a vertical axis better which may be pried open.
than a short sleeve (B),
OF THE BAR JOINT
Anterior Arrangement.--The position of the remaining teeth determines the arrangement of the bar in the mandible. The cuspids are the most resistant teeth in the lower jaw. In 57 per cent of the 270 patients for whom the bar joint was used, the two cuspids were the only remaining abutments. Within the group of two spaced anterior abutment teeth, twenty other variations are possible. Throughout this group, the bar is constructed transversely between the spaced abutments. Within the group of two adjacent anterior abutments, five different situations are possible. In this group, the Richmond copings are joined by soldering, and the bar is mounted on top of them in a transverse direction. Sag&al Arrangement.-The unilateral location of two or more remaining teeth is considerably less frequent than a bilateral location. The bar is constructed above the lateral alveolar ridge in these situations. The three degrees of freedom of movement of the bar joint remain principally the same (Fig. 32). Copings on molars generally require no pins in the root canals. An inlay that extends into the pulp chamber is cast as a part of the coping; this assures sufficient retention (Fig. 33). Diagonal Arrangement.-Diagonal placement of the bar appears possible. However, experience with fractured dentures shows that a diagonal arrangement is statically unfavorable. In these borderline situations, the bar is either bent or attached to the copings so as to attain a transverse orientation of the bar (Fig. 34).
DOLDER
J. Pros. Den. July-August, 1961
Fig. 3X-A schematic cross section shows a sagittally positioned bar. Unilateral depression results in either a rotation about the bar as an axis or an almost complete transmission of the load to the abutment teeth.
XEIXl:ORCEMENT
OF THE
BAR-COPINGS
FRAMEWORK
The bar joint denture should not be limited to instances of only two residual teeth. Planning this type of denture when more than two teeth are present helps delay the complete loss of teeth even more efficiently. Use can be made of additional remaining teeth in various ways, depending on their location. Additional incisor teeth are shortened and their copings soldered to the cuspid copings. The bar may be attached on top of the copings (Fig. 35) or in a lingual position, depending on the amount of space between the opposing teeth f~i;ig. 36 j . First premolars are joined to the cuspid copings in the same way, which substantially reinforces the abutment system. The denture base must be adequatel! excavated above the premolar copings to assure proper function of the bar joint i Fig. 371‘
Clasp and stress breaker removable partial dentures have the abutment teeth, clasps or stress breakers, and denture in horizontal sequence. This results in a visible discontinuity between natural and artificial teeth. A vertical depression of the partial denture creates an occlusal step at the junction of artificial teeth and abutment teeth and makes the discontinuity even more discernible.
Via. 33.--A.
A sagittally
arranged
bar is on the cast. B, The corresponding the sleeve in its base.
denture
contains
ii%zr141
BAR
JOINT
MANDIBULAR
703
DENTURE
The bar joint denture keeps the abutment teeth as well as the bar joint out of view underneath the denture base. Thus one esthetic problem of the usual removable partial denture is eliminated. Furthermore, the continuity of the artificial dentition of the bar joint denture leaves free choice as to size, shape, shade, and arrangement of the teeth to attain the most natural appearance possible. Remaining cuspids protrude somewhat labially from the residual ridge because of the accelerated alveolar atrophy in edentulous regions of the lower jaw. The position of the cuspid copings may thus be misleading since artificial cuspids usually must be set further lingually. The lingual prominence of the denture base resulting from a bar placed too far lingually irritates the tongue and impairs speech. The bar joint denture should be built according to approved principles of complete denture construction. Only the precise determination of vertical and centric relation, sagittal condyle paths, and interalveolar line angles permits optimal reconstruction of the dentition both functionally and esthetically. PSYCHOLOGIC
ASPECTS
The incorporation of a foreign body into the oral cavity requires an emotional adaptation which may take more or less time according to age, disposition, and environment of a patient. A complete lower denture with poor retention and inadequate masticatory efficiency will tire a patient not only physically but also emotionally. The resulting feeling of insecurity and inferiority prompts many patients not to wear the lower denture at all.
Fig.
34.-An
unusual
transversearrangement of
the bar.
The bar joint denture fits this situation perfectly. It is a denture that fills the wide gap between the clasp or stress breaker denture and the complete denture. The bar joint denture has most of the valuable assets of a removable partial denture : (1) good retention and guidance of the denture and partial stress transmission on an abutment system offer the patient safety and masticatory efficiency, (2) good appearance of the denture permits the patient an unembarrassed contact with his environment, and (3) changing to a bar joint denture delays the necessity for complete dentures for a number of years (Fig. 38). The immediate advantages of the bar joint denture render the patient’s life more pleasant for a long period of time. At the same time, the bar joint denture prepares a patient to adapt more easily to the eventual complete denture. Considering the increasing life expectancy, the need for postponing complete dentures as
704
J. Pros. Don. July-August, 1961
DOLDER
long as possible cannot be over emphasized. The drastic and still questionably successful procedures of oral plastic surgery and implant dentures should be limited to otherwise hopeless situations. STATISTIC
ANALYSIS
OF TREATED PATIENTS
For a total of 270 patients, bar joint dentures were made. Of this total, 110 patients were re-examined. These 110 patients had a mean age of 57 years and had worn the bar joint dentures an average of 3 years 3 months, but none less than 1.5 years. The examination provided a number of observations. Dpumks.-Only one of the 250 abutment teeth examined presented distinctly increased mobility. Subjectively, 97 per cent of the patients were satisfied with both appearance and masticatory performance of the bar joint denture. Abrasion of Root Copings.-The outer edge of most of the root copings showed signs of abrasion, produced by denture rotation about a sagittal or transverse axis which caused intermittent contact and friction hetween the copings and the base of the denture.
Fig. 35.-The
Fig. 36.-The
13”ig. 37.-The
copings
bar is mounted on top of the copings.
bar is positioned
lingually
on the premolar abutments reinforce the foundation
to the copings.
are soldered for the bar.
to
the
cuspid
copings
to
%%!:r’,’
BAR JOINT
MANDIBULAR
DENTURE
70.5
The amount of abrasion recorded was (1) no abrasion in 3 per cent of the patients, (2) little abrasion in 6 per cent, (3) average abrasion in 74 per cent, and (4) marked abrasion in 17 per cent. The greater abrasion was observed in dentures that had been worn for a long time and had become embedded into the tissues. Thus, the sleeves were riding directly on the bars. The process of adaptation takes a varying period of time depending on the capacity of the edentulous dental arches to bear loads. The loss of the original vertical distance of 1 mm. between the bar and sleeve occurred in more than 6 and less than 18 months in 95 per cent of the patients. To avoid unnecessary friction, the original space position of the sleeve and bar should be recreated after 1 year. The space can be obtained either by excavating the denture base over the copings or by repositioning the sleeve within the base, where possible. The sleeve is repositioned by removing the sleeve and the acrylic resin immediately surrounding it from the base. The sleeve is positioned over the bar in the patient’s mouth with the auxiliary wire interposed. After the denture has been carefully tried in over the sleeve and bar, an internal plaster key is made of the new relative position of the base and sleeve. The sleeve is incorporated in the base with acrylic resin. The copings and bar should be constructed of a hard, gold alloy. Fractures.-The incidence of fractures of bar joint dentures is higher in older dentures. The cuspid region is the most frequent site of fracture. Reinforcement of the denture base with a flat, cross-section steel lingual bar reduced the incidence of fractures and cracks from 13.7 to 6.7 per cent. Behavior of the Mucosa .--Instructions concerning proper care and cleaning of the bar-copings assembly and the denture base should be thorough. Printed instructions should be given the patient immediately after the insertion of a bar joint denture.
Fig. 38.-Complete
dentures are postponed for years by a timely transition removable partial denture to a bar joint denture.
from
a clasp-borne
inflammution: Of 110 bar-copings assemblies, 46 were well cleaned, 51 moderately so, and 13 poorly cared for. The degree of inflammation as rated by a PMA index (papillae, marginal, and attached gingivae) was related inversely to the cleanness of bar and copings. Four stages were used to rate the degree of inflammation of the mucosa: (1) unchanged, light bleeding on probing only, (2) bleeding on probing and light change of color caused by inflammatory disturbances, (3) bleeding on probing, change of color, and edematous swelling, and (4) necrosis and ulceration. The Gingivd
:oci
DOLDER
J. Pros.Den.
July-August,
1961
examination demonstrated that 57 per cent of the patients were in the first stage, 25.5 per cent in the second stage, 14.5 per cent in the third stage, and 3 per cent in the fourth stage. The mean value of PMA index was 1.63. .More commonly the denture base, being removable, was easier to clean and therefore better cleaned than the bar and copings. Although the cleanness of the denture base does not have a definite effect upon the degree of gingival inflammation. degree was found to be directly related to amount of abrasion found on the copillgs.
thzyival enlargenzent: Younger patients not only react to irritation with gingival inflammation more easily but also are more prone to hypertrophic gingival enlargement than older patients. Twelve of the 110 patients examined exhibited bGingival enlargement, particularly on papillae between neighboring copings. These enlargements receded when caustically treated with silver nitrate pearls. G‘i+l,qivaZrecession: Gingival recession was observed more frequently in older patients. Gingival recession, deepening of gingival pockets, and poor oral hygiene led to secondary decay on denuded abutments in 10 per cent of the Z-year-old restoratiolls. %uall amalgam restorations were then placed, and they proved to be adequate.
A prosthetic technique, the bar joint denture, was introduced. The denture is adapted primarily to the situation with which only a few teeth remain. This technique has been extensively tested clinically, and this report is based on statistically analyzed results on 270 patients treated and controlled regular+ over a period of 8 years. The basic construction procedures consist of (1) shortening and capping the residual teeth to render the crown : root length ratio more favorable and (2) splinting the abutments with a straight bar affixed to the cemented copings which serves. at the same time, as the bearing shaft for the complete denture. l’hc sleeve, contained invisibly in the denture base, snaps over the egg-shaped b:ir when the denture is inserted. The structure of the bar and sleeve articulation supplies retention of the denture ant1 permits the denture 3 degrees of freedom of movement. The articulation hinders the destructive horizontal displacements of the denture and permits a partial load transmission onto the abutment system. The bar joint denture offers a transitional solution between the clasp remov,+I& partial denture and the complete denture. The bar joint denture is relatively rllerpensive and improves the emotional situation of a patient at the brink of needing crmqlete dentures.
1. Brill. .h*‘.:Adaptation and the Hybrid-Prosthesis, J. PROS.DEN. 5:811, 1955. ;. DeVau, hf. M.: Biological Demands of Complete Dentures, J.A.D.A. 45:524, 1952. 5. Dolder, E. J. : Die Steg-Gelenk-Protheseim Unterkiefer, Schweiz. Monatschr. Zahn. 63:339, 19.53. 4. Dolder, EI J. : Die Steg-Geschiebe-Prothese, Zahnsrztl. Rundschau63:641, 1954.
Volume 11 Number 4
BAR
:rOINT
MANDIBULAR
DENTURE
707
5. Fisch, M. : Die Dynamik der Steg-Gelenk-Prothese, Schweiz, Monatschr. Zahn. 68:12, 1958. 6. Fisch, M. : Die Steg-Gelenk-Prothese. Statistische Bearbeitung, Schweiz. Monatschr. Zahn. 69 :845, 1959. 7. Gilmore, S. F. : A Method of R.etention, J. Allied D. Sots. 8:113, 1913. 8. Goslee, G. H.: Removable Bridgework, D. Items Interest 34:731, 1912. 9. Naucke, R. : Zur Bewahrung der Steg-Gelenk-Prothese nach Dolder, Deutsche Zahn-, Mundu. Kieferh. 27:260, 1957. UNIVERSITY OF ZURXCH DENTAL INSTITUTE PLATTENSTR. 11 ZURICH, SWITZERLAND
BAR
JOINT
MANDIBULAR
DENTURE
EUGEN J. DOLDER, DR. MED. BENT.”
University
of
Zurich, Dental Institute, Zurich, Switzerland
OF STABILITY AND RETENTION of mandibular complete dentures a solution that is universally satisfactory, especially for patients with extensive alveolar bone resorption. The smaller the number of mandibular teeth that remain, the more thoughtfully these teeth should be treated. When only two natural teeth remain, a method of preserving them is imperative. This situation occurs most frequently in three arrangements (Fig. 1) : (1) two spaced teeth in the anterior region, such as the two cuspids, (2) two adjacent teeth in the anterior segment, such as one cuspid and the adjoining lateral incisor, and (3) two spaced teeth in one posterior segment of the dental arch, such as a second molar and a premolar. The bar joint denture preserves a small number of residual teeth as long as possible. The bar splints the shortened and crowned abutment teeth, retains and partially supports the complete denture, and, together with the sleeve contained in the denture base, acts as a joint.
T is far from
HE PROBLEM
PRINCIPALOFSHORTENINGTEETH
A statically unfavorable ratio exists between the length of the crown and the length of the root in most older patients. The supported root is relatively too short (Fig. 2). Often, in addition the long isolated crown is not stabilized by adjacent teeth. Therefore, residual teeth often respond to masticatory stresses with increased mobility. However, in many instances, teeth with decayed crowns, even with the loss of vital pulp tissue, and mobile teeth can be used as abutments if the coronal parts are reduced and the roots are protected with Richmond copings (Fig. 3). Radical shortening of such teeth results in a statically more favorable ratio of the length of the crown to the length of the root and avoids further breakdown of the periodontal structures. Endodontic treatment is performed at the same time if the remaining teeth are vital. In this stage, a pulpless tooth with a well-functioning periodontium is much more important than a loose tooth with a vital pulp. PRINCIPLEOFSPLINTING
Two teeth standing separately, such as the two lower cuspids, are splinted with a straight bar attached to the two Richmond copings. The bar is positioned as close to the residual alveolar ridge as possible. Both teeth become more firm and are safer abutments periodontally than if left standing alone (Fig. 4). *Professor
of Prosthetics; Head of the Department of Fixed Partial Dentures. 689
J. Pras. Den. July-August. 1961
DOLDER
c.
R
A.
Fig. l.-Different groups of remaining teeth permit the construction of the bar joint denture. A, Two spaced anterior teeth. B, Two adjacent anterior teeth. C, Two spaced posterior teeth.
Adjacent teeth are splinted by soldering mounted on top of the copings (Fig. 5). ELEMENTS
the copings together;
the bar is
Of THE RAR JOINT
The composite bar joint is made up of the bar and the sleeve (Fig. 6). The bar consists of a straight urought wire that is egg shaped in cross section. The bar connects and splints the abutment teeth by attachment to the copings and, at the same time, functions as the shaft part of a hinge joint. The bar is always oriented with its tapered edge adjacent to the residual alveolar ridge. The bar measures 3 mm. on its major and 2.2 mm. on its minor diameter; the “microbar” measures 2.3 mm. and 1.6 mm., respectively (Fig. 6 ) _ The open-sided sleeve, which is contained invisibly in the denture base, snaps over the bar when the denture is inserted. The sleeve is a 0.2 mm. thick gold alloy
n k’@. Z--.1,
c.
The two remaining cuspids exhibit extensively decayed crowns. B and C, Roentgenograms reveal supporting bone only along a small part of the roots.
BAR JOINT
Fig.
3 .-The
remaining
teeth
are
MANDIBULAR
radically shortened, Richmond copings.
DENTURE
and
the
691
roots
are
protected
with
Fig. 4.-The two Richmond copings with parallel pins are splinted solidly by the bar. The bar is notched somewhat mesially to the copings to free the gingival crest. The open-sided sleeve, cut obliquely at the ends for the same reason, is fitted tightly between the two copings.
sheet. The sleeve fits the broad top of the bar exactly but does not quite touch the tapering sides of the bar with its elastic flanges. FUNCTIONS
OF THE BAR JOINT
The bar and sleeve joint gives retention and guides the movements of the denture relative to the abutment teeth. The sleeve supplies functionally adequate retention, and when the teeth are out of contact, there is a vertical gap of about 1 mm. between the roof of the sleeve and the top of the bar (Fig. 6). From this initial (resting) position, the bar and sleeve joint permits three possible movements of the denture : (1) during vertical depression of the denture, the entire sleeve is translated toward or upon the bar, (2) during unilateral depression of the denture, only the more depressed end of the sleeve touches the bar, and (3) rotation about the bar as an axis is possible for approximately 10 degrees in either direction from the resting position. Rotation is limited only gradually by the elastic flanges of the sleeves (Fig. 6). MATERIAL
The alloys for all components of the bar joint should provide the requisite mechanical characteristics, including permanent elasticity of the sleeve. I use a high quality, platinum-containing alloy of gold.* *The Scientific
Dental Co., Ltd., Los Angeles, Calif.
J. Pros. Den. July-August, 1961
DOLDER
69 :!
Fig. B.-The
bar is mounted on top of two adjacent abutment
roots
Fig. G.---The bar joint in schematic cross section shows, from left to right: the parts disnssembled, insertion of the denture, the position of rest, perpendicular depression of the whole denture. and rotation about the bar as an axis.
4.
B.
F’ia. i.--&4. Low Richmond copings with long pins are used on long roots. copings on short roots require, in addition to short pins, a central inlay preparation lir~v!ration of the root for adequate retention.
B, Richmond and a higher
Construction tarp’a har joint denture when only the lower cuspids remain ilin-:trates the procedures. i~Ind,doutic treatment is iollowrtl 1)~ shortening and preparation of the abutIIIC’III>, iitting of pins ( which must be parallels, making of individual copper hand impressions with pills. and temporary sealing of the roots. Copings are waxed 1111 ~qqw-plated dies, invested, and cast around the pins, which are then soldered :ogerl~r. ShJrt roots with consequentlv short pins should be prepared somewhat Iiig-!wr am1 possibly with an interior re&orcing inlay preparation to achieve good rtwniion of the copings (Fig. 7 1,
BAR ,JOINT
Fig. K-The
MANDIBULAR
copings are positioned
DENTURE
in the individual
693
plaster impression.
An individual acrylic resin impression tray is prepared on a preliminary lower cast. Sufficient space is provided for the Richmond copings. The tray is fitted in the mouth, and the borders are developed in the same manner as for complete dentures. The Richmond copings are placed on the abutment teeth, and a plaster impression is made. The copings are positioned in the impression (Fig. 8) I An impression of the upper jaw is made if a maxillary complete denture is to be constructed at the same time. After the casts are poured, occlusion rims are constructed. The jaw relation records are made, and the teeth are selected.
Fig. 9.-A,
The labial
plaster
key contains
the anterior the cast.
teeth.
B,
The key
is positioned
on
The teeth are positioned in the occlusion rims. Acrylic resin teeth are used in the lower anterior segment so they can be arranged directly above the residual alveolar ridge. The try-in is completed. The position of the lower anterior teeth is recorded with a labial plaster core, and the anterior segment of the wax pattern is removed. The teeth are left fixed in the plaster key (Fig. 9). The bar is fitted between the two abutment copings on the cast and positioned horizontally with the tapered edge toward and close to the alveolar ridge, at right angles to the line bisecting the angle formed by the posterior alveolar ridges (Fig. 10). An oblique position of the bar impairs correct function
J. Pros. Den. July-August, 1961
1mL,Ixm
Fig.
IO.-The
Fig. 11 .-The
l;ig
1?,-.4
bar is positioned
horizontal
positioning
perpendicularly posterior
to a line ridges.
bisecting
of the bar and sleeve is important. R, The correct position.
the
angle
between
.4, The incorrect
schematic cross section of the anterior part of the cast illustrates the position bar and sleeve relative to the alveolar ridge and the artificial teeth.
Fig. 1X-The
soldered bar-copings
framework
is reseated onto the cast.
the
position.
of the
BAR JOINT
Fig. 14.-Three
dovetailed
MANDIBULAR
DENTURE
flaps are cut into the open-sided sleeve and bent up to supply tion in the acrylic resin denture base.
695
reten-
Fig. 15.
Fig. 16. Fig. 15.-The sleeve is fixed temporarily on the bar in the resting position by an intermediary wire. Fig. 16.-The copings are covered with a 1 mm. layer of plaster prior to curing the denture. Unimpaired functioning of the bar joint is not possible when the denture base flts the copings closely.
Fig 17.-An enlarged schematic cross section of the bar joint shows, from top to bottom: retentive Raps of the sleeve, the intermediary wire, the bar, the sleeve, and the plaster which assures the correct position of the sleeve during curing of the denture and creates space that is needed for proper functioning of the bar joint.
DOLDER
J. Pros. Den. July-August, 1961
of the joint (Fig. 11). The microbar is used only where there is insufficient interocclusal clearance for the regular size bar. The bar is temporarily attached to the cast with sticky wax or self-curing resin, and the plaster key containing the anterior teeth is carefully repositioned. The position of teeth determines whether or not the bar must be repositioned further lingually (Fig. 12). The final position of the bar and the copings is determined on the cast and secured with plaster. The bar and copings are solidly soldered and replaced on the cast, and the clearance between the bar and the mesial gingival papilla is determined (Fig. 13). An appropriate length of the metal sleeve is cut, and dovetailed flaps are bent up for retention in the denture base. No soldering is required, and thus the elasticity of the sleeve is fttlly maintained (Fig. 34). An auxiliary wire is placed between the top of the bar and the sleeve to maintain their position during the curing of the denture ( Fig. 15 I
pig.
‘ig.
‘ig.
Fig. IX.-The anterior teeth are delinitely wpositioned with the plaster key. Fig. 19.-A small lingual bar is adapted to reinforce the denture base. Fig. 2K-The functioning and the retention of the bar joint are tested outside
the mouth.
Volume I1 Number 4
BAR JOINT
Fig. Zl.-The
denture
Fig. 22.-The
Fig. 23.-The
MANDIBULAR
DENTURE
base above the abutment copings must be sufficiently free movement of the bar joint.
cemented copings with the connecting
697
excavated
to allow
bar are placed in the mouth.
elastic flanges of the egg-shaped sleeve may be tightened with instrument for better retention of the finished denture.
a suitable
pointed
The Richmond copings are covered with a 1 mm. layer of plaster (Fig. 16), and the space between the alveolar ridge and the flanges of the sleeve is also filled with plaster to maintain space in the denture base (Fig. 17). The anterior teeth are repositioned on the cast using the plaster key (Fig. 18), and the wax pattern of the denture is completed with a reinforcing lingual bar (Fig. 19). The flasking is completed in the usual manner. After processing, the denture is carefully deflasked; especially the bar must be cautiously removed from the sleeve.
598
J. Pros. Den. July-August, 1961
DOLDER
The anterior lingual part of the denture is made as thin as possible. Free functioning of the joint is tested outside the mouth with the bar-copings framework inserted into place in the denture base (Fig. 20). The denture base may need additional relief above the Richmond copings (Fig. 21) . The bar-copings framework is trial fitted in the mouth; slight grinding of the pins may be necessary to ensure correct, parallel seating (Fig. 22). Roentgenographic examination of the abutments and temporarily seated copings is required to establish the proper fit. The free flanges of the sleeve are tightened if the finished denture lacks adequate retention (Fig. 23). The occlusion is carefully balanced. Adjustment appointments are given the patient for 1 and 4 weeks after insertion. At the same time, the instructions to the patient regarding cleansing are repeated. IrYKhMICS
OF THE
BAR
JOINT
DENTURE
The mandibular bar joint denture is a complete denture on a fixed partial denture (microbridge) supported by terminal abutments. The bar and the sleeve
Fig. 2~1. Fig. 24.-A schematic cross section resting go&ion. Note the vertical gap bar. Fig. 25.-A schematic cross section vertically depressed position. Note that
Fig. 25.
shows the anterior part of the completed denture in its of about 1 mm. between the roof of the sleeve and the shows the anterior part of the completed denture in a the “roof” of the sleeve touches the top of the bar.
Fig. Z&---In a recently inserted bar joint denture, there is a vertical gap of about. 1 mm. between the bar and the roof of the embracing sleeve. Unilateral depression of the denture results in hinge movement about the axis (R) somewhere in the ridge of the undepressed side. Only the more depressed end of the sleeve touches the bar, while the opposite end remains near its resting position. The rotating system may be called a one-sided lever system.
Volume 11 Number 4
BAR JOINT
MANDIBULAR
DENTURE
699
serve as the connecting elements of the two dentures. The fixed partial denture consists essentially of the bar that is attached to the abutment copings. This constitutes the male part of the complete restoration. The female part, the sleeve, is contained in the base of the removable complete denture. The insertion and removal of the denture are accomplished easily by the patient. The elastic flanges of the sleeve readily snap over the egg-shaped bar and give the denture adequate retention. Position of Rest.-The inserted denture rests on the alveolar ridges and is entirely tissue borne. In this rest position, the roof of the sleeve is about 1 mm. above the top of the bar (Fig. 24). Vertical Translation.-When the denture is depressed vertically, it presses upon the resilient mucosa of the posterior ridges. The entire length of the sleeve approaches and then is depressed onto the bar transmitting part of the masticatory load onto the abutment teeth (Fig. 25). Th us, in the final phase of vertical depression, the denture is supported partly by the abutments and partly by the soft tissue. A well-retained and well-guided denture that transmits part of the masticatory load to anterior abutment teeth is appreciated by the patient, particularly during use of the anterior teeth.
Fig. 27.-A long bar ensures better guidance and retention of the denture than a short bar. Note the favorable lever diagram of the more nearly parallel posterior ridges (A) as compared to the diverging posterior ridges [B).
Fig. 28.-After the process of adaptation, the denture has embedded itself into the tissue approximately 1 mm., and the sleeve rests on the bar in its entire length in the resting position at this time. The hinge axis of a unilateral depression of the denture is now the coping of the depressed side, while the opposite side of the denture is slightly lifted from the mucosa. The rotating system may now be called a two-sided lever system.
J. Pros. Den. July-hugust, 1961
Fig. PR.-The
posteriorly
depressed denture rotates about the bar as its axis.
I!nilateral L)epressiolj.--The bar and sleeve permit the unilateral depression of the denture when it occurs during unilateral mastication. The denture rotates about the undepressed ridge as an axis, and the corresponding end of the sleeve remains near its rest position. Only the loaded end of the sleeve is depressed toward the bar (Fig. 26j. The longer the bar and the sleeve can he made, the better are the retention and the guidance of a denture subjectecl to such rotation (Fig. 27). In the course of 6 to 12 months, the denture embeds itself approximately 1 mm. into the mucosa, allowing the sleeve to rest directly upon the bar. The axis of rotation in unilateral depression of the clcnture is then transferred to the loaded el~d of the sleeve, and unilateral depression results in a slight lifting of the denture from the mucosa of the opposite side (Fig. 28 ) .
Fig. XJ.--The undesirable movements 01’ the denture are impeded by the bar joint: (‘a) lateral Imnslation; (RJ sagittal translation: (~1 horizontal rotation about a rertic*al axis in the anterior rvni9!i.
i’os~c~~io~I,c,fi~c,ssiolr.--Cl~e~~ing on the posterior part of the denture results in rot:ltion about the bar, its axis. This rotation is possible about any axis throughout tl~ continuum of axes within the perpendicular translation (Fig. 29). .I11 of these motions of the denture occur normally during mastication. The eggshaped structure of the bar joint permits these three movements and guides the rlc:lturt> effectivell,. However. the construction of the bar joint eliminates undexir:Ale movernent~ of the denture which are ultimately destructive (Fig. 30). I,atrral translatory movements hasten alveolar atrophy of the posterior ridges. The flatter the ridges are initially, the more care should be taken to impede lateral
Volume 11
BAR JOINT
Number 4
MANDIBULAR
DENTURE
701
translatory movements. A correctly fitted sleeve that touches both copings makes lateral displacement of the denture impossible. Forward and backward translations are withstood by the snugly fitting sleeve. Such movements can also be minimized by extending the denture base distally onto the retromolar pads. Rotation about a vertical axis in the anterior region is primarily destructive to the posterior ridges and impairs masticatory efficiency because the denture escapes the chewing force. Efficiency of chewing and stability of the denture are again to some degree dependent on the length of the bar and sleeve (Fig. 31). Extending the denture base into the mylohyoid region decreases the tendency of the denture to make such rotations.
Fig. 31.-A
long sleeve (A) hinders
ARRANGEMENT
rotation about a vertical axis better which may be pried open.
than a short sleeve (B),
OF THE BAR JOINT
Anterior Arrangement.--The position of the remaining teeth determines the arrangement of the bar in the mandible. The cuspids are the most resistant teeth in the lower jaw. In 57 per cent of the 270 patients for whom the bar joint was used, the two cuspids were the only remaining abutments. Within the group of two spaced anterior abutment teeth, twenty other variations are possible. Throughout this group, the bar is constructed transversely between the spaced abutments. Within the group of two adjacent anterior abutments, five different situations are possible. In this group, the Richmond copings are joined by soldering, and the bar is mounted on top of them in a transverse direction. Sag&al Arrangement.-The unilateral location of two or more remaining teeth is considerably less frequent than a bilateral location. The bar is constructed above the lateral alveolar ridge in these situations. The three degrees of freedom of movement of the bar joint remain principally the same (Fig. 32). Copings on molars generally require no pins in the root canals. An inlay that extends into the pulp chamber is cast as a part of the coping; this assures sufficient retention (Fig. 33). Diagonal Arrangement.-Diagonal placement of the bar appears possible. However, experience with fractured dentures shows that a diagonal arrangement is statically unfavorable. In these borderline situations, the bar is either bent or attached to the copings so as to attain a transverse orientation of the bar (Fig. 34).
DOLDER
J. Pros. Den. July-August, 1961
Fig. 3X-A schematic cross section shows a sagittally positioned bar. Unilateral depression results in either a rotation about the bar as an axis or an almost complete transmission of the load to the abutment teeth.
XEIXl:ORCEMENT
OF THE
BAR-COPINGS
FRAMEWORK
The bar joint denture should not be limited to instances of only two residual teeth. Planning this type of denture when more than two teeth are present helps delay the complete loss of teeth even more efficiently. Use can be made of additional remaining teeth in various ways, depending on their location. Additional incisor teeth are shortened and their copings soldered to the cuspid copings. The bar may be attached on top of the copings (Fig. 35) or in a lingual position, depending on the amount of space between the opposing teeth f~i;ig. 36 j . First premolars are joined to the cuspid copings in the same way, which substantially reinforces the abutment system. The denture base must be adequatel! excavated above the premolar copings to assure proper function of the bar joint i Fig. 371‘
Clasp and stress breaker removable partial dentures have the abutment teeth, clasps or stress breakers, and denture in horizontal sequence. This results in a visible discontinuity between natural and artificial teeth. A vertical depression of the partial denture creates an occlusal step at the junction of artificial teeth and abutment teeth and makes the discontinuity even more discernible.
Via. 33.--A.
A sagittally
arranged
bar is on the cast. B, The corresponding the sleeve in its base.
denture
contains
ii%zr141
BAR
JOINT
MANDIBULAR
703
DENTURE
The bar joint denture keeps the abutment teeth as well as the bar joint out of view underneath the denture base. Thus one esthetic problem of the usual removable partial denture is eliminated. Furthermore, the continuity of the artificial dentition of the bar joint denture leaves free choice as to size, shape, shade, and arrangement of the teeth to attain the most natural appearance possible. Remaining cuspids protrude somewhat labially from the residual ridge because of the accelerated alveolar atrophy in edentulous regions of the lower jaw. The position of the cuspid copings may thus be misleading since artificial cuspids usually must be set further lingually. The lingual prominence of the denture base resulting from a bar placed too far lingually irritates the tongue and impairs speech. The bar joint denture should be built according to approved principles of complete denture construction. Only the precise determination of vertical and centric relation, sagittal condyle paths, and interalveolar line angles permits optimal reconstruction of the dentition both functionally and esthetically. PSYCHOLOGIC
ASPECTS
The incorporation of a foreign body into the oral cavity requires an emotional adaptation which may take more or less time according to age, disposition, and environment of a patient. A complete lower denture with poor retention and inadequate masticatory efficiency will tire a patient not only physically but also emotionally. The resulting feeling of insecurity and inferiority prompts many patients not to wear the lower denture at all.
Fig.
34.-An
unusual
transversearrangement of
the bar.
The bar joint denture fits this situation perfectly. It is a denture that fills the wide gap between the clasp or stress breaker denture and the complete denture. The bar joint denture has most of the valuable assets of a removable partial denture : (1) good retention and guidance of the denture and partial stress transmission on an abutment system offer the patient safety and masticatory efficiency, (2) good appearance of the denture permits the patient an unembarrassed contact with his environment, and (3) changing to a bar joint denture delays the necessity for complete dentures for a number of years (Fig. 38). The immediate advantages of the bar joint denture render the patient’s life more pleasant for a long period of time. At the same time, the bar joint denture prepares a patient to adapt more easily to the eventual complete denture. Considering the increasing life expectancy, the need for postponing complete dentures as
704
J. Pros. Don. July-August, 1961
DOLDER
long as possible cannot be over emphasized. The drastic and still questionably successful procedures of oral plastic surgery and implant dentures should be limited to otherwise hopeless situations. STATISTIC
ANALYSIS
OF TREATED PATIENTS
For a total of 270 patients, bar joint dentures were made. Of this total, 110 patients were re-examined. These 110 patients had a mean age of 57 years and had worn the bar joint dentures an average of 3 years 3 months, but none less than 1.5 years. The examination provided a number of observations. Dpumks.-Only one of the 250 abutment teeth examined presented distinctly increased mobility. Subjectively, 97 per cent of the patients were satisfied with both appearance and masticatory performance of the bar joint denture. Abrasion of Root Copings.-The outer edge of most of the root copings showed signs of abrasion, produced by denture rotation about a sagittal or transverse axis which caused intermittent contact and friction hetween the copings and the base of the denture.
Fig. 35.-The
Fig. 36.-The
13”ig. 37.-The
copings
bar is mounted on top of the copings.
bar is positioned
lingually
on the premolar abutments reinforce the foundation
to the copings.
are soldered for the bar.
to
the
cuspid
copings
to
%%!:r’,’
BAR JOINT
MANDIBULAR
DENTURE
70.5
The amount of abrasion recorded was (1) no abrasion in 3 per cent of the patients, (2) little abrasion in 6 per cent, (3) average abrasion in 74 per cent, and (4) marked abrasion in 17 per cent. The greater abrasion was observed in dentures that had been worn for a long time and had become embedded into the tissues. Thus, the sleeves were riding directly on the bars. The process of adaptation takes a varying period of time depending on the capacity of the edentulous dental arches to bear loads. The loss of the original vertical distance of 1 mm. between the bar and sleeve occurred in more than 6 and less than 18 months in 95 per cent of the patients. To avoid unnecessary friction, the original space position of the sleeve and bar should be recreated after 1 year. The space can be obtained either by excavating the denture base over the copings or by repositioning the sleeve within the base, where possible. The sleeve is repositioned by removing the sleeve and the acrylic resin immediately surrounding it from the base. The sleeve is positioned over the bar in the patient’s mouth with the auxiliary wire interposed. After the denture has been carefully tried in over the sleeve and bar, an internal plaster key is made of the new relative position of the base and sleeve. The sleeve is incorporated in the base with acrylic resin. The copings and bar should be constructed of a hard, gold alloy. Fractures.-The incidence of fractures of bar joint dentures is higher in older dentures. The cuspid region is the most frequent site of fracture. Reinforcement of the denture base with a flat, cross-section steel lingual bar reduced the incidence of fractures and cracks from 13.7 to 6.7 per cent. Behavior of the Mucosa .--Instructions concerning proper care and cleaning of the bar-copings assembly and the denture base should be thorough. Printed instructions should be given the patient immediately after the insertion of a bar joint denture.
Fig. 38.-Complete
dentures are postponed for years by a timely transition removable partial denture to a bar joint denture.
from
a clasp-borne
inflammution: Of 110 bar-copings assemblies, 46 were well cleaned, 51 moderately so, and 13 poorly cared for. The degree of inflammation as rated by a PMA index (papillae, marginal, and attached gingivae) was related inversely to the cleanness of bar and copings. Four stages were used to rate the degree of inflammation of the mucosa: (1) unchanged, light bleeding on probing only, (2) bleeding on probing and light change of color caused by inflammatory disturbances, (3) bleeding on probing, change of color, and edematous swelling, and (4) necrosis and ulceration. The Gingivd
:oci
DOLDER
J. Pros.Den.
July-August,
1961
examination demonstrated that 57 per cent of the patients were in the first stage, 25.5 per cent in the second stage, 14.5 per cent in the third stage, and 3 per cent in the fourth stage. The mean value of PMA index was 1.63. .More commonly the denture base, being removable, was easier to clean and therefore better cleaned than the bar and copings. Although the cleanness of the denture base does not have a definite effect upon the degree of gingival inflammation. degree was found to be directly related to amount of abrasion found on the copillgs.
thzyival enlargenzent: Younger patients not only react to irritation with gingival inflammation more easily but also are more prone to hypertrophic gingival enlargement than older patients. Twelve of the 110 patients examined exhibited bGingival enlargement, particularly on papillae between neighboring copings. These enlargements receded when caustically treated with silver nitrate pearls. G‘i+l,qivaZrecession: Gingival recession was observed more frequently in older patients. Gingival recession, deepening of gingival pockets, and poor oral hygiene led to secondary decay on denuded abutments in 10 per cent of the Z-year-old restoratiolls. %uall amalgam restorations were then placed, and they proved to be adequate.
A prosthetic technique, the bar joint denture, was introduced. The denture is adapted primarily to the situation with which only a few teeth remain. This technique has been extensively tested clinically, and this report is based on statistically analyzed results on 270 patients treated and controlled regular+ over a period of 8 years. The basic construction procedures consist of (1) shortening and capping the residual teeth to render the crown : root length ratio more favorable and (2) splinting the abutments with a straight bar affixed to the cemented copings which serves. at the same time, as the bearing shaft for the complete denture. l’hc sleeve, contained invisibly in the denture base, snaps over the egg-shaped b:ir when the denture is inserted. The structure of the bar and sleeve articulation supplies retention of the denture ant1 permits the denture 3 degrees of freedom of movement. The articulation hinders the destructive horizontal displacements of the denture and permits a partial load transmission onto the abutment system. The bar joint denture offers a transitional solution between the clasp remov,+I& partial denture and the complete denture. The bar joint denture is relatively rllerpensive and improves the emotional situation of a patient at the brink of needing crmqlete dentures.
1. Brill. .h*‘.:Adaptation and the Hybrid-Prosthesis, J. PROS.DEN. 5:811, 1955. ;. DeVau, hf. M.: Biological Demands of Complete Dentures, J.A.D.A. 45:524, 1952. 5. Dolder, E. J. : Die Steg-Gelenk-Protheseim Unterkiefer, Schweiz. Monatschr. Zahn. 63:339, 19.53. 4. Dolder, EI J. : Die Steg-Geschiebe-Prothese, Zahnsrztl. Rundschau63:641, 1954.
Volume 11 Number 4
BAR
:rOINT
MANDIBULAR
DENTURE
707
5. Fisch, M. : Die Dynamik der Steg-Gelenk-Prothese, Schweiz, Monatschr. Zahn. 68:12, 1958. 6. Fisch, M. : Die Steg-Gelenk-Prothese. Statistische Bearbeitung, Schweiz. Monatschr. Zahn. 69 :845, 1959. 7. Gilmore, S. F. : A Method of R.etention, J. Allied D. Sots. 8:113, 1913. 8. Goslee, G. H.: Removable Bridgework, D. Items Interest 34:731, 1912. 9. Naucke, R. : Zur Bewahrung der Steg-Gelenk-Prothese nach Dolder, Deutsche Zahn-, Mundu. Kieferh. 27:260, 1957. UNIVERSITY OF ZURXCH DENTAL INSTITUTE PLATTENSTR. 11 ZURICH, SWITZERLAND